During the electrical charging of batteries, water is electrolyzed during charging. In order not to reduce the service life and performance of the battery, water must therefore be refilled regularly into the battery cells. This is often achieved by means of water-refill plugs plugged into the fill opening of the battery cover and connected in series with the aid of conduits. These water-refill plugs close automatically when the fill level in the battery cells has reached the desired point. The fill level in the cells is often determined with the aid of floats. The movement of the float is transferred to the valve body via a rod assembly, so that the valve closes when the desired fill level has been reached, as is known from WO 83/00260 [U.S. Pat. No. 4,512,378].
As a result of the charging and discharging processes, impurities form in the battery cells that float on the electrolyte surface and deposit on the parts of the refilling plugs that come into contact with the electrolyte. This can lead to sticking of the rod assembly and thus to the malfunctioning of the refilling plug.
A water-refill plug is known from DE 35391671 where the upper head of the float forms the valve body and, in its upper position, seals the valve seat. A retaining element projects upward on the head of the float body, rests with a ferromagnetic part against a permanent magnet, and is held thereby in this position. Detachment is achieved by means of a pressure pulse transmitted through the refill conduit.